I'm going to be echoing a lot of what OP said, but I'd like to take a stab at why this kind of stuff bothers some men. Basically it seems to contradict some of the principles put forth by feminism/post-modernism that moderates/liberals have come to grudgingly accept.

Lots of men knew that when they said "women are so shallow!" or "watch out, women are gold diggers", they were not talking about all women. They knew they were complaining about what they perceive to be a societal problem perpetuated by some women. But then they were told that generalizations, even if they are clearly framed as such, can be harmful, and can be perceived and internalized as universals by the less-than-critical audience who is receiving them. The intent didn't matter, the output and its raw effects mattered. A remark might well have come from a place of genuine frustration. In fact, most racist/sexist BS probably does. But we all agree that the fact that it came from genuine frustration is not a justification for its effects. Now people are seeing charges of anti-masculne/anti-white sentiment excused with "I was just venting" or "I was expressing my frustration". And while most people can see that anti-white sentiment is not harming society the same as anti-black sentiment, they aren't sure how this translates into differing standards for excuses.

Another major lesson to come from modern feminist though / "PC culture" is that its the hurt feelings that matter, not the intentions of the 'hurter'. In the course of life, we're all liable to hurt somebody's feelings at times, but the correct response, we've been told, is not to try to reason with the persons feelings, or tell them that they have incorrectly interpreted the hurtful statement and to update their feelings to reflect the 'correct' interpretation. Actually, I think a decent amount of moderate men would actually disagree with this, and say intention /should/ factor in. But even those men are lost when they see this being applied to them, while the opposite (feelings need no justification) is being applied to women.

Basically, I think the issue is a perceived hypocrisy. There is a standard applied to women that is not applied to men. Now, the usual response to this is that the situation is asymmetrical, that misogyny is not the same as misandry, and its left at that. I think the problem is a lot of guys, even if they accept this, don't see how specifically that negates these principles they've grudgingly swallowed. "It's not the same!" is just not as perceived as a satisfying response. It can come across like hand-waving. Even the last sentence 'does that help clarify things', while I know was written in a perfectly friendly way, would go over like a lead balloon if a man used it after explaining to a women why she should not be offended about something.

Let me just say that personally, I'm not offended by any of these generalizations. Hell, if I found myself offended by a trending "#rapeBeatAndTortureUselessMen" hashtag, it would be time for some serious self-reflection. I don't care if a woman hates men. I don't care if she thinks men are weak. I don't care if somebody wants to commit genocide against all men. I just don't. I think instead what irks some of the moderates is again just the seeming double standard.